Fighting the U-boats

Merchant ships

The Liberty ship Jeremiah O'Brien

During the Battle of the Atlantic in the early years of
World War II, the German U-Boats were sinking allied
merchant ships at an alarming rate. Unless more ships
were built to replace those sunk, the war effort would grind to a
halt. Cargo ships would have to be replaced faster than the
U-Boats could sink them. In May 1941, the rate of German
sinkings of merchant ships was more than three times the
capacity of British shipyards to replace them, and more than
twice the rate of combined British and American shipyard output
at the time.

One of the most effective way to defeat the German tonnage-war was to build more ships than the Germans could sink.